Prediction of Phosphorous Concentration in Effluent of Recirculating Aquaculture Systems

摘要

An unsteady-state model for predicting dissolved phosphorous (DP) concentration in the effluent of a single RAS was developed, The input parameters are daily feed rate, make-up "water flowrate, and volume of the system. The phosphorous wasted by the fish is calculated using the feed phosphorous content (1.2 wt%), feed conversion ratio (0.9), and phosphorous retention of the fish (4.32 g/kg fish). The dissolved portion of the total phosphorous rejected by the fish is the digestible portion (55%) lessthat retained by the fish, and amounts to 30% of the rejected phosphorous. The residual 70% remains with the solids. The model assumes that the water is well-mixed, there is no leaching of the phosphorous contained in the fish faeces, there is no excessfeed, and the make-up water flowrate is constant. The concentration of DP in the effluent is determined from the weighted cumulative daily feed rates. Model predictions are compared with experimental data collected over several months at a recir -culating salmon-smolt hatchery and indicate that dissolution of phosphorous may be occurring in the septic tank used to store the waste solids.